Capacity responsive system



Dec. 6, 1949 SIMONs 2,490,238

CAPACITY RESPONSIVE SYSTEM Filed Jan. 4, 1946 6 Sheets-Sheet 1 Farr/m 4/ ic /1552101 h; AW? hmV/WV Dec. 6, 1949 H. M. snvloNs CAPACITY RESPONSIVE SYSTEM Filed Jan. 4, 1946 6 Sheets-Sheet 2 hm W Dec. 6, 1949 H, M. SIMONS CAPACITY RESPONSIVE SYSTEM 6 Sheets-Sheet 3 Filed Jan. 4, 1946 MMM-W H. M. SIMONS CAPACITY RESPONSiVE SYSTEM 6 Sheets$heet 4 Dec. 6, 1949 Filed Jan. 4, 1946 i w J74 1115 y Hwy 4 hmr/ Dec. 6, 1949 H. M. slMoNs CAPACITY RESPONSIVE SYSTEM 6 Sheets-Sheet 5 Filed Jan. 4, 1946 Dec. 6, 1949 s o s 2,490,238

CAPACITY RESPONSIVE SYSTEM Filed Jan. 4, 1946 6 Sheets-Sheet 6 a MAW 5*. hwgzv Patented Dec. 6, 1949 z,4sm,23a

UNITED STATES PATENT o- FlcE CAPACITY RESPONSIVE SYSTEM Harry M. Simons, Langhorne, Pa., assignor to Gage B. Ellis, Langhorne, Pa.

Application'January 4, 1946, Serial No. 639,123

2 Claims. 1

This invention relates to capacity-responsive electrical systems, and more particularly to systems which operate in response to capacity changes of .an antenna produced by some condition, such as the presence of a person or object in the vicinity of the antenna. The invention relates more especially to a novel balance-type antenna system which is adapted .to respond to capacity changes or variations that disturb the normal condition of balance or predetermined unbalance. 1

In a capacity-responsive system, it is desirable to provide for different sensitivities according to the different specific uses to which the system may be applied. In some instances, as where the system is used for burglar protection and the antenna is in the form of a window screen, low sensitivity is desirable to prevent undesired operation in response to opening and closing of the window. In other instances, as where the system is used to indicate or record the number of persons who view an advertising display, high sensitivity maybe desired in order that the system will operate in response to the presence of a person in the general vicinity of the display. In still other instances, intermediate degrees of sensitivity may be desired.

It is also desirable that such a system be adaptable for operation either in response to a capacity increase or a capacity decrease, depending upon the specific manner in which the system is to be used in a given instane.

In the case of a balance-type system, it is further desirable that the system shall be capable of being readily adjustable to different conditions. In some instances, it may be desired to provide a condition of exact balance, while in others it may be desired to provide a condition of predetermined unbalance. But since the antenna may take various forms and sizes depending on the particular installation, the desired easy and accurate adjustability has heretofore been impossible of achievement.

The principal object of the present invention is to provide a capacity-responsive system which possesses all of .the aforementioned desirable characteristics as well as others hereinafter mentioned.

Another object of the invention is to provide a system which is insensitive to voltage variations.

Still another object of the invention is to provide a system which will respond to excessive temperature as well as to the presence of a person or object.

A further object of the invention is to provide lator l5 of the tuned plate type.

v2 I a system which enables the capacities of two antennas to be balanced against one another, thereby enabling the same system to be used with .the two antennas either of which will detect the presence of a person or object.

Other objects and features of the invention will be apparent from the following detailed description.

In the accompanying drawings I Fig. 1 is a schematic illustration of embodying the present invention;

Fig. 2 is a schematic illustration showing a a system preferred form of the rectifying arrangement em- Fig. 3 is a schematic illustration of another embodiment wherein the capacities of two antennas are balanced against one another; and

Fig. 4 to '7 show. different examples of installations wherein the system of Fig. 3 may be employed.

Referring first to Fig. 1 of the drawings, there is provided a high frequency transformer ll having a center-tapped primary winding 12, and a tuned secondary winding Hi. If desired, the transformer may be of the adjustable core type, as indicated, to facilitate tuning thereof to a particular frequency. An adjustable tuning condenser Hl may be connected across the secondary winding to tune the same to the desired-frequency.

A source of high frequency oscillations is connected between the center tap of the primary winding and ground. In the specific illustration, the said source is shown'as comprising an oscil- Such oscillator comprises a vacuum tube. It whose plate is connected to a coil H which is inductively coupled to a grid coil l8 to provide the necessary feedback action. The plate coil l1 and the associated condenser constitute the tank circuit which determines the frequency of oscillation. The condenser 20 and the resistor 2| are the usual grid condenser and grid leak, respectively. The oscillator is connected between the center tap of winding l2 and ground by means of the coupling condenser 22 and resistor 23. Preferably the oscillator is designed to operate at a frequency of termined unbalance so that there is normally a voltage across the secondary winding. A ilx'ed capacitor 25 is connected between the upper end oi the primary winding l2 and ground. A similar capacitor 26 of substantially equal value is connected between the lower end of winding l2 and ground. An adjustable balancing capacitor 21 is connected in shunt relation with capacitor 26 and an adjustable resistor 25 is also connected in shunt relation with capacitor 25. A plurality of capacitors, numbered 29 to 33, having different capacitance values, each has one of its plates connected to the upper end of the primary winding i2. Terminals 34 to 25 are connected to the other plates of these capacitors. A terminal 39 is connected directly to the upper end of the primary winding i2. This arrangement enables the antenna 24 to be connected to any one of the various terminals so that the antenna may be connected to any one of the capacitors 29 to 35, or it may be connected directly to the upper end of winding i2 by means of the terminal 99. To this end, a terminal 49 may be connected to the antenna for connection to any one of the above mentioned terminals. Alternatively, a selector switch may be provided, in which case the terminals 34 to 39 may take the form of stationary switch contacts, and the terminal 49 may take the form of a movable switch contact adapted to engage any one of the stationary contacts. Obviously, the provision of a selector switch will facilitate connection of the antenna to any one Of the capacitors 29 to- 32, or to the upper end of winding l2 directly.

It will be noted that when the antenna is connected, there are two parallel capacitive paths between the upper end of winding I 2 and ground, one path including the capacitance of capacitor 25 and the other including the capacity of the antenna. There are also two parallel capacitive paths between the lower end of winding I2 and ground, including capacitors 26 and 21, respectively. Since the capacitors 25 and 26 are substantially equal, the adjustable capacitor 2'! serves to balance the capacity in shunt with the capacitor 25, or to provide a desired degree of unbalance. The purpose of the adjustable resistor 28 is to balance the antenna resistance where necessary.

The circuit arrangement enables accurate balancing of the capacities connected to the opposite ends of the primary winding l2, and it also enables the attainment of diflerent degrees of sensitivity. The capacitors 29 to 33 provide a range of selectable supplementary capacitances which serve to vary the resultant capacity in shunt with capacitor 25. By varying the capacity 1 in series with antenna 24, the resultant capacity in shunt with capacitor 25 may be varied in relation to that of capacitor 25. The smaller the series capacity, the smaller will be the resultant capacity in relation to that of capacitor 25 and the lower will be the sensitivity of the system. As the series capacity is increased, the resultant capacity is increased and the sensitivity is increased.

In any instance, the antenna to be employed may be connected to different ones of the terminals 24 to 39 and the adjustable elements 21 and 28 may be varied to obtain the desired sensitivity and the desired condition of balance or predetermined unbalance. With the circuit prperly adjusted, any capacity variation which disturbs the normal condition will produce a voltage or changein voltage across the secondary winding It. The resultant voltage may be rectifled. amplified, and supplied to an indicator or alarm apparatus, such as that shown in copending application, Serial No. 639,121, filed January 4, 1946, now Patent No. 2,479,274, issued August 16, 1949. since the present inventionis not concerned with the subsequent portion of the system, the elements thereof are merely represented in block form at 4|, 42 and 45.

The system shown in Fig. l'can be adjusted so that there is normally no voltage across the secondary winding l3, and any capacity change which disturbs this condition will produce 9. voltage across said winding. The system may also be adjusted so that there is normally a small voltage across the secondary winding, and some capacity changes will produce an increase of said voltage while other capacity changes will produce a decrease of said voltage. Both a voltage increase and a voltage decrease may be caused to operate the apparatus being controlled. It should be borne in mind that the antenna 24 may be of such character that its capacity decreases in response to some action, as for example the opening of a vault door.

It will be'noted that any change in the operating voltages applied to the oscillator l5 will not produce a voltage across the secondary winding l3, since the opposed voltages across the two halves of the primary winding l2 will vary by the same amount.

The system may be made to serve for the detection oi excessive temperature changes, such as those due to a fire, by providing a capacitor 44 and a normally open switch 46 forming part of a thermal responsive device 45. Actuation of device 45 will cause connection of capacitor 44, which will disturb the normal condition.

The values of the various elements may be chosen according to the expected range of antenna capacities which may be encountered in the particular use to which the system is to be applied.

Fig. 2 shows the preferred form of rectifying means which has been employed in a system embodying the present invention. As illustrated, the rectifying means may comprise a diode 41 and load resistors 49, 49 and 50 having associated by-pass condensers 5| and 52. The voltage across resistor 50 may be applied to an amplifying tube 53 by means of a coupling condenser 54 and resistor 55. The rectifying system is described more fully in copending application serial No. 639,122, filed January 4, 1946, now Patent No. 2,481,954, issued September 13, 1949. As there pointed out, the system is somewhat unusual but it has been found from actual usage to be highly desirable.

In Fig. 3 there is shown another embodiment of the invention which enables the balancing of the capacities of two antennas employed with the same system. The elements corresponding to those of Fig. 1 are designated by the same reference characters and require no further description. In addition to such elements, a plurality of capacitors, numbered 56 to 68, having different capacitance values, each has one of its plates connected to the lower end of the primary windin; l2. Terminals ii to are connected to the other plates of these capacitors, and an additional terminal 66 is connected directly to the lower end of winding I2. A second antenna 51 may be connected to any one of these terminals, by means of a connecting terminal 68. In this instance also, a selector switch may be employed,

as previously described. The system may be adjusted by connecting the antennas 24 and 61 to difierent ones of their associated terminals, and by varying the adjustable elements 21 and 28.

In the system of Fig. 3, the arrangement may be such that the system responds to increase in the capacity of antenna 24 or to increase in the capacity of antenna 61. The system may be slightly unbalanced, so that an increase in the capacity of antenna 24 will cause an increase in the voltage across the secondary winding l3, while an increase in the capacity of antenna 61 will cause a decrease in said voltage. Such voltage changes may not only serve to indicate disturbance of the normal condition but may also indicate from which side the disturbance originated.

If desired, the system may be made to respond to excessive temperature variations, such as would be caused by a fire, by providing the previously mentioned elements 44 to 46 in conjunction with antenna 24, and by providing a temperature responsive switch device 69 in conjunction with the second antenna 61. It will be obvious that operation of either of the thermal responsive switches will cause response of the system.

The adaptability of the system in Fig. 3 to various installations is illustrated in Figs. 4 to 7. Fig. 4 is a schematic sectional plan view of a room or other enclosure having built-in antenna members. The illustration shows the fioor l and the four walls 1| to 14. The wall 13 has a door opening 15, while wall 14 has windows 18 and I1. One of the antennas employed in the system of Fig. 3 comprises interconnected screen or like elements 18 and 19 built into the walls Fig. illustrates the application of the two antenna system to two different rooms represented at 83 and 84. plate or screen shown in dotted outline at 85 built into or beneath the fioor of room 83 in the vicinity of the doors 86. The other antenna comprises a metal door structure 81 within the door opening 88 in room 84. The antenna plate 85 may be insulated from ground, as shown in Fig. 6, by means of insulating support members such as shown at 89.

Fig. 7 illustrates a similar application of the system to two rooms or enclosures shown at 90 and 9|. One of the antennas comprises metal shelving 92 in room 90, while the other antenna comprises metal shelving 93 in room 9|.

Thus it will be seen that the two-antenna system of Fig. 3 has wide application and makes it possible to utilize a single system for the protection of a plurality of areas.

From the foregoing description, it will be apparent that the system or network provided by the invention is readily adaptable to various uses and conditions, and has various desirable features. As previously stated, the values of the elements may be selected according to the expected range of antenna capacities. By way of example and with reference to Fig. 1, the antenna might comprise one or more window screens and might have a capacity within a range One antenna comprises a of 50 to 300 micro-microfarads, in which case the values of the principal elements may be as follows;

25-4000 micro-microfarads 26950 micro-microfarads 21730 micro-microfarads 281 megohm 29-750 micro-microfarads 30-500 micro-microfarads til-250 micro-microfarads 32-100 micro-microfarads 33-50 micro-microfarads While the invention has been described with reference to certain embodiments and arrangements, it will be understood that the illustrations and description are only for the purpose of disclosure and are not intended to limit the invention.

I claim:

1. In a capacity-responsive electrical system, a transformer having a center-tapped primary winding, a source of high frequency oscillations connected between the center tap of said winding and ground, a plurality of capacitors having different capacitance values connected to one end of said winding, means for connecting a first antenna to any one of said capacitors, a plurality of capacitors having difl'erent capacitance values connected to the other end of said winding, and means for connecting a second antenna to any one of said last-mentioned capacitors.

2. In a capacity-responsive electrical sytem, a transformer having a center-tapped primary winding, a source of high frequency oscillations connected between the center tap of said winding and ground, a fixed capacitor connected between one end of said winding and ground, an adjustable capacitor in shunt with said fixed capacitor, a plurality of capacitors having difierent capacitance values each having one of -its plates connected to the said end of said winding, terminals connected to the other plates of said last-mentioned capacitors, a terminal connected directly to the said end of said winding, whereby an antenna may be connected to any one of said terminals, a fixed capacitor connected between the other end of said winding and ground, a plurality of capacitors having different capacitance values each having one of its plates connected to said other end of said winding, terminals connected to the other plates of said lastmentioned capacitors, and a terminal connected directly to said other end of said winding, wherebya second antenna may be connected to any one of the latter terminals.

HARRY M. SIMONS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,658,953 Theremin Feb. 4, 1928 1,701,975 Gunn Feb. 12, 1929 2,262,766 J ansson Nov. 18, 1941 2,312,306 Bierwirth Mar. 2, 1943 2,388,576 Seeley Nov. 6, 1945 OTHER REFERENCES Electronic Protective Systems" appearing on pp. 367-374 of Electrical Engr. for Oct. 1944. 

